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Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

1973 Kawasaki H2 750 Running Lean Responses


Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as your subject. 

1973 Kawasaki H2 750 Running Lean Responses 

A: I received several emails from a few folks in response to the “Kawasaki H2 750 Is Running Lean” question (Keith’s Garage, May/June 2012) who have more experience with these bikes than I do. They pointed out that I may have missed the problem of a bad crankshaft seal on the left side of the engine. The left side runs in air and, if leaky, will suck air into the left cylinder transfer space, causing a severe lean condition. I’ll let them explain.  

First up is Leigh Nelson, who writes:  “Though your explanation was very informative, you might have overlooked another problem. The left crankshaft seal is to the outside and could have failed. It may be drawing in air there. The right side is in the clutch cover, and if it failed it would draw oil and you would oil-foul the plug, plus it would smoke heavily.”

Dave Webster adds: “On the carbs you should have had him look at the carb slide balance as well; if the left slide is heavily open before the other two it will lean it out. An easy way to check this is to remove the airbox inlet tubes at the carbs, wind the slides up so that the center one is even with the top of the carb mouth, then lock the throttle and check it against the other two. Speaking of those air inlet tubes, they should be checked for leaks/holes or poor fitment, as that can lead to lean running as well by bypassing the filter and allowing more air in that way. If that’s the original airbox, then the rubber is likely deteriorating.” Thanks guys. I appreciate the feedback and advice from experienced Kawasaki mechanics. MC